Be aware that if youu do rent it out and the three months they need to stay turns into a few extra months, the moment they are in the house for 6 months plus 1 day, they are entitled to a Part 4 tenancy, (i.e. a four year tenancy, irrespective of what type of lease you wish them to sign). If you want rid of them after that, you can give them notice based on your desire to move in (section 2 of Residential Tenancies Act) but if they dispute it, it will take the PRTB a minimum of a year to hear your case and you will still need to go to the District Court to turf them out as the PRTB won't bother.
Sorry to sound negative but I would run a mile from this. If they need to stay in the house til their renovations are finished, the chances are that they will do so - you have no control over how long their renovations will take and therefore no real control over when they leave. If that is ok with you, then offer to rent them the house - if not, then don't!